1. Field of the Invention
The present invention relates to a press die set for forming a flange that bends an edge of a panel at a right angle in a press-forming direction and an edge adjacent to the edge at a negative angle and a flange forming method.
2. Description of the Related Art
Many automobile parts are formed by press working. Such parts include door parts that have a flange formed along the edge thereof. In many cases, the flange of the door part or the like is formed by right-angle bending, which is a technique of bending an edge of a panel at approximately a right angle in the press-forming direction. However, negative-angle bending is sometimes used, which is a technique of bending a panel at an angle greater than a right angle to cover the expanded portion of the lower die. In general, the panel bent at a negative angle is difficult to eject from the die set. Thus, in flange formation involving the negative-angle bending, a rotary cam type press die set, a double cam type press die set or the like, from which the panel can be easily ejected, is often used for press working. However, for press working of door panels, hood panels or the like that have an edge bent at a right angle in the press-forming direction and an edge adjacent to the edge bent at a negative angle, there are proposed working apparatus or methods that do not use the rotary cam type press die set, the double cam type press die set or the like, which are complicated and expensive.
For example, in Japanese Utility Model Publication No. 6-49375, there is proposed a composite pressing apparatus that can perform right-angle bending and negative-angle bending of an automobile hood panel at the same time in one step and has a mechanism for ejecting the worked panel from the lower die. It is described that the part of the composite pressing apparatus that is responsible for flange formation is movable, so that the panel can be easily released. In order to appropriately bend the boundary part between the negative-angle part and the right-angle part, many composite pressing apparatus including the apparatus described above have a cam bending blade for negative-angle bending having a substantially L-shaped profile and is configured so that a part of the edge bent at a right angle by a press bending blade is bent at a right angle by the cam bending blade, and the operation of the press bending blade slightly lags behind the operation of the cam bending blade. The term “one step” indicates the operation of the upper die which lowers to the lower die and then rises to the original position.
However, such composite pressing apparatus have a problem that deformation, such as strain and fracture, due to the difference in timing between the operation of the press bending blade and the cam bending blade is likely to occur. Japanese Patent No. 3013684 proposes a composite pressing apparatus that solves the problem. More specifically, Japanese Patent No. 3013684 proposes a composite pressing apparatus comprising a press bending blade that bends one of two adjacent edges of a curved workpiece in the same direction as the direction of pressing of an upper die and a cam bending blade that bends the other of the adjacent two edges at a negative angle inwardly with respect to the pressing direction of the upper die, in which the press bending blade has a movable bending blade at a part that overlaps with the cam bending blade during press working, and the adjacent two edges are bent at the same time by avoiding interference between the cam bending blade and the press bending blade by retracting the movable bending blade when the cam bending blade moves downward.